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Ensign Wasps Don't Sting People, but Will Kill Cockroaches

Steve has been an online writer for over nine years. His articles often focus on the wildlife of Tenerife.

Ensign Wasps Are Harmless

The ensign wasp (Evonia appendigaster) looks a bit like a black spider with wings. Many people, upon seeing one, might assume that it will sting, but in fact, it is totally harmless.

The ensign wasp is actually a beneficial insect because it is a parasite of cockroaches and hunts for their egg cases, which are known as oothecae. The female wasps lay their eggs in them and the wasp larvae eat the cockroach eggs.

An ensign wasp

An ensign wasp

The Evaniidae Family

Ensign wasps are in the family Evaniidae and get their name because they move their abdomens up and down as if they are signaling with a flag. They are also known as Hatchet Wasps.

Adults are about 1/4 to 3/4 inch long and can be found feeding on the nectar of flowers and on the honeydew that aphids have deposited on leaves, as well as hunting for cockroach egg cases.

Besides living in Tenerife and the Canary Islands, they are also found in the U.S., Canada, and many other parts of the world. They have followed where cockroaches have gone.

The larva of an ensign wasp eats all the eggs it finds in an ootheca and then pupates inside the egg case.

Adult female ensign wasps often come into houses searching for oothecae. Unfortunately, many people kill them, thinking they are harmful pests when the truth is just the opposite. So if you see one, don't destroy it. Either leave it alone or put it outside. It may not look like it, but it is an insect that can be helpful!

Avispa bandera. Ensign wasps (Evania appendigaster)


Manuela on August 29, 2018:

According to Wiki, these things have been around since the dinosaurs. I'm 48 and have never seen one in my entire life until this last year. Initially I saw it on the wall across the room and thought it was a spider. Then when I saw it closer, I thought, nope, a small cricket. I believed it to be a cricket until it suddenly flew across the room! Then I had to find out what it was. This house had previously been infested with roaches, we saw evidence of that after removing vents to repaint some of the rooms after we bought the house. I saw a few (roaches) in the kitchen a few months later and sprayed for them and haven't had a problem since. But here lately, we're seeing more and more of these wasps in the house. I live in Florida and roaches are abundant here. Having a lot of trees in my back yard provides a haven for them. We also have Palmetto bugs which are like a huge version of a roach and they get inside the house as well. I wonder if the Ensign Wasp feeds on their eggs as well? As long as they keep the roaches at bay, I'm ok with it! I've woken up with bites, but we have mosquitoes, various house spiders, it could be a number of things that feed on us in the night. Unless it's actually on me and stings me, I'm not accusing it lol.

Chris on August 06, 2018:

Bummer, I feel bad now. I've never seen these odd looking bugs ever before in Arizona where I was born and raised. That is until about two months ago where I've found three in my apartment in Gilbert, AZ. I've killed them because they looked to be some sort of wasp and fly mixed into one new bug and I was not sure what it was or if it could harm me and my dogs. As much as I hate roaches, we have sewer roaches here near me in this lake community I live in and If I knew before that it was harmless, I definitely would have simply let it outside.

Tiffany on June 14, 2017:

These guys are a little intimidating to me but honestly so is a butterfly that flies to close to me, I know they're beneficial but I hate having them in my home. I live in a house that was once a haven for cockroaches, due to it's previous tenant's uncleanliness so when we first moved in I used to see them all the time. I haven't seen one in almost two years until today when I saw two of these wasps on the sliding glass door, but we don't have anymore cockroaches in our home. Thank goodness! I'm thinking they came in, to hide from the rain. I live in a town house and the neighbor to my right also lives in a pretty cluttered and dirty home like the old tenants of my house, so I'm also thinking and am pretty sure they have a cockroach problem usually I see them crawling outside my backyard around their wall, and at night the rats use my fence to hop on to their wall and go into their utility room, probably hunting the cockroaches too either way they're nasty pests and I'm happy to see the ensign wasp outside of my house where they belong, unfortunately for them today they found themselves in my house and were brutally murdered by my grandmother who came to visit.

Jordan on May 14, 2017:

I moved one of these off my pants onto the back of my hand by letting it crawl onto it, then after examining it for 2 whole minutes I let it go. No sting. You'd have to do some serious provoking to be stung by one of these docile wasps.

Tyson on December 05, 2016:

They do sting.thats what made me research what they were. "THEY DO STING" OH,AND IT HURT AS WELL.

Steve Andrews (author) from Tenerife on February 20, 2016:

I think it is some other insect.

patty on September 15, 2015:

Im from miami at the hospital now been bit by one it flew up my dress stung me it felt like a lil fire flew on me from a ciggerate i had i grabed my dress. With this same bag kelt it n bought it in with no im on meds thigh swole so yes they do sting and down here they are hard to kill u really dont see thrm often and when u do u only see 1

Austin Davis on July 21, 2015:

I saw one of these in my room and i decided not to screw with it, it flew into my light multiple times but got out multiple times, window shut door open, go to sleep and i wake up with a sting on my knee.

ArinHouston on July 05, 2015:

I usually just kill the ones I see because of the annoying way they fidget and fly around. But after reading that they eat roach larvae I was happy and decided I'd let them stay around in my house unless they bother me and get in my personal space. I've never been stung by one, even when I approached it and tried to smack it around a bit. They don't chase me but they may fly towards and past me in an attempt to get away. They're so delicate though! One smack kills them so fast! So I don't really think of them as threats. More like annoying helpers. Like mosquito hawks. I live in Houston TX and while we do have plenty of roaches here, coastal cities like Corpus don't have these things around as much- they could sure use them! Roaches EVERYWHERE.

Daphne on January 21, 2015:

These things are gross and I killed about 3 of them inside my room in just one week!! I just found out what they are and I probably should of moved them to the outside but I am terrified of these. They just relax on my walls instead of hiding. I use to call them hulk mosquitoes because they look like a mosquito on steroids. My mother said that these left a red mark on her arm when she was sleeping in my room this week like a sting, even though they say these wasps don't bite..... but who knows.

Sara on December 14, 2014:

Love these guys, and even more so now that I know what they eat. I used to call them "cricket-mosquitoes" before I found out what they were called, because they looked like the lovechild of a mosquito and some sort of grasshopper.

I'm in Texas, and I've never been stung by one, even when I actively pester them into crawling on my hands. (They usually just get fed up and fly away.)

Kayla on July 12, 2014:

Here in Texas I believe we may have a adapted species, I was stung by one last week. But the sting wasn't too terribly bad. It is definitely the same type of bug. I watched it sting me, not knowing what it was, or what it was doing.

Chelsey on May 28, 2014:

The ones in Houston, Tx sting.

Rick on March 27, 2014:

I have these wasps all around my yard and house and not a single one has stung me even when provoked.

Steve Andrews (author) from Tenerife on August 11, 2012:

Why do they not sting other people? How did they come to sting you? Even ordinary wasps and bees need to be provoked.

Megan on August 10, 2012:

I've been stung twice by these inside my house, just FYI. It is undoubtably the same insect, because I caught both of them after stinging me and have also seen others around the house.

Steve Andrews (author) from Tenerife on April 26, 2012:

This site also states that they do not sting so maybe it was some other insect?

susan on April 25, 2012:

well my son wasn't asleep and the one he encountered did sting him

Steve Andrews (author) from Tenerife on September 02, 2011:

Not according to books it can't! If you were asleep how do you know what it was?

Dan on August 31, 2011:

Ensign wasps CAN stung me over my eyelid while I was asleep; similar to a fire ant sting.